1. Field of the Invention
The present invention relates to a capacitive touch-sensitive panel.
2. Discussion of Related Art
Object Detection methods currently used in a touch screen mainly includes a resistive method, a surface acoustic wave method, surface capacitive method and a projected capacitive method. In case of the projected capacitive method, multi-touch detection is possible, and excellent durability and visibility can be exhibited, and therefore the projected capacitive method has been adopted as a main input means of a portable mobile device.
The capacitive touch screen controller may detect changes in an amount of electric charges charged in capacitive sensors on a touch screen panel by user interference to recognize a user input, and be classified into a self-capacitive method and a mutual-capacitive method in accordance with an electric charge accumulation method. The self-capacitive method configures a single conductor per a capacitive sensor to form an electric charge surface with a reference ground outside the sensor while the mutual-capacitive method allows two conductors on the touch screen panel to mutually form electric charge surfaces so as to serve as a capacitive sensor.
In general, self-capacitive method uses X/Y orthogonal type conductor arrangement, and in this case, each capacitive sensor serves as a line sensor, and therefore only one axial information of X location and Y-location are provided from each of an X-line sensor group and a Y-line sensor group every time when the touch screen is scanned. Thus, in the self-capacitive touch screen, detection and tracking of a single touch may be possible, but a multi-touch may not be fully supported. The mutual-capacitive method also uses the X/Y orthogonal type conductor arrangement, but is different from the self-capacitive method in that each capacitive sensor is provided in the form of a grid sensor at each location where X conductor and Y conductor cross each other and responses of all the grid sensors are sensed independently when a user input is applied on the touch screen. Each grid sensor provides a response which corresponds to one-X/Y location and is independent to each other, and therefore, in the mutual-capacitive touch screen, user input information may be extracted from an X/Y two axial information set provided by an X/Y grid sensor set, thereby detecting and tracking the multi-touch applied by a user can be accomplished.
A configuration of a conductor of a general mutual-capacitive touch screen panel and a detection method thereof will be herein described. First electrodes including a conductor extending in any one direction and second electrodes including a conductor extending in a direction orthogonal to the first electrodes form a mutual-capacitive sensor through a dielectric material between the two electrodes. A capacitance C of the mutual-capacitive sensor is defined as C=∈*a/d when a distance of the two electrodes is ‘d.’, an area of an electric charge surface is ‘a’, and an equivalent dielectric constant of all dielectric materials existing between electric charge surfaces is ‘∈’, and has a relationship of Q=CV with an amount Q of electric charges accumulated on the mutual-capacitive sensor and a potential difference V applied to two electrodes/electric charge surfaces to induce charge accumulation. When a user approaches a sensor, interference to an electric field formed between the two electrodes may occur to prevent a part of electric charges from being accumulated on the sensor, and therefore an amount of electric charges accumulated on the sensor may be reduced, thereby reducing the capacitance. This may be understood as a change in the capacitance caused by a change in an equivalent dielectric constant between the electric charge surfaces due to the user's approach to the sensor, but the actual physical phenomenon that happens is that a part of the electric field between the electric charge surfaces is shunted due to the user's approach so that the amount of electric charge accumulated on the surfaces are reduced. When applying an AC waveform to one electric charge surface of the sensor by connecting an AC voltage source to the first electrode, variation (ΔQ) of ΔQ=CΔV in the amount of electric charge with respect to the capacitance C which varies in accordance with a degree of the user's approach to the sensor may occur, and the charge variation may be converted into a current or a voltage form by a read-out circuit connected to the second electrode. Such converted information may be generally subjected to signal processing operations such as noise filtering, demodulation, digital conversion, accumulation, and the like to be used in a coordinate tracking algorithm and a gesture recognition algorithm. An example of a capacitive touch-sensitive panel is described in U.S. Pat. No. 7,920,129.
In a conventional electrode configuration, a contact area between an object for applying a touch input to a touch panel and a cover window in contact with the object is large enough for a plurality of sensors to participate in performing touch detection, thereby touch coordinates extracted and gestures recognized are relatively smooth and stable. However, when a touch input is applied by a child's finger or a woman's finger with a relatively small cross-sectional area, only a limited number of sensors may participate in performing touch detection, and therefore incorrect touch coordinates may be extracted, or an incorrect trajectory may be traced due to non-linear response to movement of an object.